Control system for tap changing regulator



Aug. 13, 1963 v c. w. NIELSEN 0, 5

- CONTROL SYSTEM FOR TAP CHANGING REGULATOR 7 Filed New 17. 960 2 Sheets-Sheet 1 EJMWlsoA v I .Bfiorrlfw 1 C. W. NIELSEN Aug. 13, 19 63 3,100,865 v CONTROL SYSTEM FOR TAP CHANGING REGULATOR 2 Sheeis-Sheet 2 Filed Nov. 17. 196 0 aw -e/fwm/Zw MW QLXl'oMw/y pli'ngs have been used.

United States Patent 3,100,865 CONTROL SYSTEM FOR TAP CHANGING REGULATOR Charles W. Nielsen, Eagle, Wis, assignor to Allis- This invention relates to a voltage regulating system and in particular to a control system for a step type regulator having coarse and fine step mechanisms.

With increased use of electronic equipment in modern industrial processes, close control of operating voltages has become extremely important. This is particularly true in electro-chemical industries where voltage rectifiers are used to control electrolytic refining. In such applications the voltage applied to the rectifier must be closely controlled in fine steps in addition to coarse steps and quite frequently available over a wide range.

To achieve fine regulation over a wide range through the use of mechanical tap changing regulators fine step windings have been employed. A line step winding has been connected between taps on the coarse step transformer winding and, similar to the manner in which contacts are changed on the coarse winding, has a mechanical tap changing mechanism. In such a manner the voltage range between a pair of adjacent taps on the coarse winding of the transformer can be divided into a number of finer steps.

In providing a voltage regulator with two mechanical tap changing mechanisms synchronization of the two would make it impossible to supply uniformly increasing fine steps. if the contacts on thetfine step winding start on a second cycle without any movement of the contacts on the coarse winding a sudden change in voltage equal to the potential across a pair of taps on the coarse mechanism will occur. While synchronization could be accomplished by having an operator stand by the regulator ready to move the contacts on the coarse winding whenever necessary, automation is more desirable. To automate the mechanisms, expensive and'bulky mechanical cou- The invention described herein overcomes the disadvantages of expense, size and maintenance encountered ice and apparatus for transformers embodying'the present invention;

in the use of mechanical couplingssuch as gears through I a novel and unique arrangement of electrical switches.

Through a minimum number of switches arranged in a predetermined fashion the two tap changing mechanisms are synchronized so that interruption of a load current and other undesirable occurrences are avoided.

It is therefore one object of this invention to provide a new and improved voltage regulating mechanism.

Another object of this invention is to provide a new and improved voltage regulating mechanismcapable of operating over a wide voltage "range in either coarse or extremely fine and uniform steps.

' A further object of this invention is to provide a new and improved voltage regulating mechanism having an automatic electrical control system for synchronizing a a FIG. 2 is a schematic showing of the control system for synchronizing the tap changing mechanisms; and

FIGS. 3 through 5 are tables illustrating the sequence of operation of the switches in the controlsystem of FIG. 2. I

The voltage regulating system illustrated in FIG. 1 is capable of operating through a range of zero to maximum voltage and comprises a coarse mechanism 11 and a fine mechanism 12 associated with an autotransformer 13.

1 Coarse Step Mechanism The autotransformer .13 comprises a core 15, an exciting winding 16 and a coarse tapped series winding 17 electrically and inductively connected to the exciting winding. in the particular embodiment, the coarse winding 17 is in a bucking or substracting relationship with the exciting winding '16 and is divided into seven equal portions which are connected to circular arranged stationary contacts1-8 on the coarse tap changing mechanism 11. Rotatably coupled together are a pair of movable coarse contacts 21a and 21b which are positioned in a conventional manner to make contact with the stationary contacts 18 of the coarse mechanism.

Fine Step Mechanism The line step tap changing mechanism 12 which provides small steps of voltage change is electrically connected to the coarse mechanism 11 through a pair of leads connected to the pair of movable contacts 21a and 21b on the coarse mechanism. Fine winding -23 may be wound on the same core 115 containing the exciting winding and coarse winding; For the purpose of explaining the operation of the inventiomthe fine winding 23 should be considered as being in a boosting or additive relation- "ship with the coarse winding .17. However, if desired th polarityof the line winding may be reversed.

In a conventional manner the fine winding is associated with nine stationary contacts 25 arranged in a circular pattern. Thepotential across a pair of these contacts is, in the particular embodiment, equal to of the potential across a pair of adjacent coarse taps 18. A second pair of movable contacts 26a and 26b are positioned to make cont-act withthe stationary contacts '25 of the fine winding. A preventive autotransformer 27 is connectedacross the pair of movable contacts 26a and 26b on the fine winding in order to prevent short circuiting of a tapped portion of the winding. Thus, the output'o-i the voltage regulating apparatus appears across terminal 2-9 connected to the midpoint of the preventive autotnans- 'forrner 27 andian' end 30 of the exciting winding 16. During eachcoarse step the fine-mechanism movable contacts rotate through a null cycle, providing 18 fine steps numbered 71 through 88. l

Control System for Fine Step Operation With reference to FIG. 2, a control system 32 is provided for synchronizing the fine and coarse mechanisms.

This system includes apair of tap changing motors 34 and 35, one tor the coarse. mechanism 11 and theother for the fine mechanism 12. A power supply 36 is pro- .vided for driving the two motors. e5;

p p The control system which includes a raise circuit 39 and a lower circuit 39' may be designed to actuate the tap changing mechanisms in response to either manual or automatic control, by

means of a conventional sensing device.

The sensing I device has not been shown for purposes of clarity and may be any of a number of the devices designed to interpret voltage line conditions and provide an impulse to the control indicating that a raise in voltage is desired. The a other switch 42 closes upon a lower signal. Connected to the raise and lower switches are corresponding sets of raise switches B1, NBl, N132 and lower switches B1, B2 and NBI'. These switches open and close in response to the position -which the movable contacts 21a and 2112 on the coarse mechanism assume. On the raise circuit 39, switchesNBl and N132 close in response to nonbridging positions of the coarse, mechanism. By nonbnidgi-ng it is means that both of the movable contacts 210: and 21b of the coarse mechanismare on one tap contact 18.

The third switch B1 of the raise circuit is closed in response to a bridging condition or, that is, when the pair of movable contacts 21a and 2117 on the coarse mechanism straddle two tap contacts 18. The lower circuit 39 includes a pairof bridging switches B1 and B2 and one nonbridg-ing switch NBl'. One of several ways in which these bridging and n-onbridging switches can be made responsive to the positioning'of the coarse movable contacts 21a and 21b is to arrange them on a rotatable drum which is simultaneously driven with the coarse movable contacts.

Connected between the bridging and. nonbridging switches and raise and lower windings. 44, 44, 45, 45' of the two drive motors 34 and35 is a setof motor switches M which complete and interrupt current pathstothe fine and coarse motors. Each of the lower and raise windings in each of the motors has a pair of switches associated with it. Thus, for the raise winding 44 of the coarse motor 34 switch M1 is connected to the coarse mechanism bridging switchBl with switch M2 being connected tocoarse mechanism nonbridging switch NB1. These motor switches M are responsive'to the positions 71 through 88of the movable contacts 26A and 26B of the fine mechanism. Again, this may be accomplished by arranging the switches ona rotatable drum coupled to the finernotor 3'5.

' Transfer Mechanism I In the particular embodiment the output voltage may be changed in 30*4'steps from to 105.6% rated voltage. However; torapidly increase the output from one level, such as 25% to a substantially greater level, such as 75% a transfer mechanism 47v is provided. In FIG 1 a pair'of movable transfer or bypass contacts 48a and 48b are shown connected between the coarse movable contacts 21a and 21b and the fine mechanism 12.v By moving 'thesebypass contacts from their fine position on stationary contacts 50a over to the coarse positions on stationary contacts 50h with motor 51 the fine'mechanisrn' 12 and "its preventive autotransformer 27 are bypassed. A second 7 larger preventive autotransformer 52M-becomes connected to the coarse winding-17 and theco'arse mechanism may now be operated through the entire voltage range in only 32 steps-instead of the fine operation covering 304 steps.

In order that the load cnrrentis not interrupted. during movement of the bypass contacts 48a and 4% there must be synchronization between the transfer mechanism,

and both the fine and coarse mechanisms ll and 12. Referring to FIG. 2, a manual push button switch. 54 is connected between the raise and lower circuits, 39. and 39 anda switch M5 connectedto one sideof the power supply and responsive to the fine mechanism. Con-- nected t- -one side of thepower supply is a finemechanism responsive switch M6. Switches M5 and'M6 may 'bemounted'on the same drum. containing theother M .switchesp To synchronize the transfer mechanismwith' the coarse mechanism switch B3 is connectedto switch ,M3. Switch B3 is closed when coarse movable contacts tables.

21a and 21b bridge a pair of contacts 18. A pair of raise and lower transfer switches 56 and 56 which may be manually controlled are connected to switch B3. Switch motor 34. Switches 63 and 6-3" may be actuated by the same means that operates switches 56, 56' and 57.

Fine Step Operation FIGS. 3, 4 and 5 illustrate the sequence in which the above described M switches close in response to the tap changing mechanisms. While explanations are directed toward a raise operation, it is to be understood that the lower operation functions in a reverse manner. On one axis of the table the M switches are set forth and on the other axis the eighteen positions (71-88 partially shown in FIG. 1) inwhich the fine tap changing mechanism 26a and 26b assume are set forth. The shaded areas indicate when a particular M switch is closed. Likewise, FIGS. 4 and 5 show the sequence of switches 58 through 61 and switches 56, 56', 57, 63, 63'.

A brief operation of the control system can be'readily explained through reference to FIGS. 1, 2 and 'thethree With the particular type of illustrated windings, the pair of movable contacts 21a and 21b on the coarse mechanism are generally on a nonbridging position while the pair of contacts. 26a and 2612 on the fine winding produce fine step voltage changes through a sequence of bridging and nonbridging positions. It will be observed as the fine mechanism movable contacts move from non bridging position 87 to bridging position 88, the load current flows only through the leading coarse contact 21a. Thus, keeping in mind that the fine winding 23 is in additive relationship with the coarse winding. 17,, it can be seen that if the leading contact 21a of the coarse mechanism is still in a nonbridging position there will bea sud-den drop of voltage when the fine contacts assume position 88 instead of obtaining a fine increase in voltage.

If the various switches in the control system are arranged in accordance to the sequence of FIGS. 3 through 5', the above condition can be avoided. It is to be noted that .at position 84 of the fine mechanism, an additional switch M2 is closed. Assuming that the impulse from the sensing device calls for an increase in voltage the closing of switch M2 causes an advance in the movable contacts 21a and 21b of the coarse mechanism. .While the illustrated coarse mechanism contacts B1, N131, etc., areall shown in an open position it is to berecalled that half of these switches will always 'be closed since thexcoarse mechanism contacts will either be in a bridging or nonbridging' position. Consequently, since the coarse mechanism is normally in a nonbridging position. all of the nonbridging switches NB1 NB2 and NBl will be closed and, with the additional closing of switch M2, current is supplied to the raise winding 44 of the coarse mechanism motor 34.

With the advance of the coarse mechanismfcontacts to a bridgingposition, the nonbridging switches open andv thebridging switches B1, B1 and B2 close; In such a manner the coarse motor is able to drive the coarse mechanism only one step unlessotherwise called for. Thus,

bridging position and the fine mechanism contacts 26a and 26b at position 88, current-flows through the leading contact 21a of the coarse mechanism; Likewise, this leading contact 21a carries the load current as the fine mechanism goes into position 71.

But, as the fine mechanism continues to cycle'and move into position 72, the load current is carried by the second coarse movable contact 21b. Thus, it the second movable coarse contact Zlb is still in a bridging position there will be a sudden drop in output voltage as the fine mechanism moves to position 72. This drop would be nearly equal to the potential across adjacent contacts 18 on the coarse winding and is an undesirable condition. Therefore, there must be assurance that the second contact 215 of the coarse mechanism moves into a nonbridging position with the leading contact 21a prior to movement of the fine mechanism into position 72 and subsequent to leaving position 88.

As can be observed from the table in FIG. 3, switch M1, which is connected to abridging coarse switch B1, closes when the fine mechanism reaches position 71. Upon closing of switch M1 current flows through the closed bridging switch B1 and through the raise winding 44 of the coarse motor, thereby obtaining an advance in the second contact 21b. With the coarse contacts now in a nonbridging position, the fine mechanism continues onto position 72, etc. and a steady uniform voltage increase is obtained.

With respect to switch M3 which is connected to the raise winding 45 of the fine mechanism motor it will be noted that this switch is open only at position 71 of the fine mechanism. This switch further assures that as long as the coarse mechanism contacts 21a and 21b are in a bridging position the fine mechanism will not be able to advance farther than position 71' thereby assuring avoidance of load current interruption.

In a similar manner, svtutch M4 also provides an additional safeguard against load current interruption. It will be noted that this switch is open only when the fine mechanism is in'the position 87. Consequently, as long as the coarse mechanism contacts are in a nonbridging position, M4 prevents movement of the fine mechanism from position 87 to position 88.

The function of thesecond nonbridging switch NB2 I is to avoid overdriving the coarse mechanism. Thus, at

positions 85 and 86'wl1enthe coarse mechanism is in a bridging position with switch M2 closed, thehypothetical connection of switch M4 to the nonbridging switch NB];

i would cause'the coarse mechanism to continue moving as a currentfiow would occur through switches B1, M3,

M4 and M2 to the coarse raise winding 44. Likewise,

the particular arrangement of switches calls fora second bridging switch B2 in the lower circuit to avoid overdriving the coarse contacts 21a and 21b through the taneously close.- Inasmuch as switch 58 isal-ready closed" (see FIG. 4) current flows through windin 65 ot' the transfer motor 5 1 and bypasscontact -48a'movesto 'oontact 50b, assuming an intermediate position. Switch 6 1 opens as it is also responsive to the positioning of the transfer mechanism. Consequently, prevention of current to the fine mechanism is fully assured. V

The transfer motor continuesto run and bypass sw-i-tcll 48b moves to contact 50b, thus bypassing the fine mecha- 6 position, switch so closes and current is supplied to the coarse motor tor providing coarse steps. To return to fine step operation the above procedure is reversed.

Through the (above descnibed control system a compact and dependable regulating unit is provided which may operate in either. uniformly fine or coarse steps through an extremely wide range.

,the present invention has been illustrated and described, it will be apparent to those skilled in the art thatmodifications other than those shown'may be made Without depanting from the spirit of the invention or from the scope of the appended claims. For example, the illustrated moving switches may be replaced by static elements for controlling current flow without departing from the spirit of the invention.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. A wide range fine step voltage regulator comprising a coarse step tap changing unit and a fine step tap changing uni-t mechanically independent of each other, each said unit having a winding with a plurality of taps with circular arranged stationary contacts connected thereto and a pair of movable contacts driven by a motor for successively engaging said stationary contacts, said movable contacts of said coarse unit being connected to the tapped winding of said fine unit, and an electrical control system for synchronizing each said motor and said mov- 'able contacts in each'said unit comprising current limiting means responsive to the positions of said movable contacts relative to their respective stationary contacts whereby load current in said regulator is maintained throughout cycling of said movable contacts by each said motor.

2. A wide range fine step voltage regulator comprising a coarse step tap changing unit and a fine step tap changing unit, each said unit having a winding with a plurality of taps with circular arranged stationary contacts connected thereto and a pair of movable contacts driven by a motor for successively engaging said stationary contacts,

said movable contacts of said coarse unit being connected I to the tapped winding of said fine unit, and an electrical control system for synchronizing said movable contacts in each said innit comprising switching means connected between apowersupply and each said motor, said switching means being responsive to the positions of said movable contactsrelative to their respective stationary contacts Q whereby load current in said regulator is uninterrupted throughout cycling of said movable contacts by each said motor. i

3. In combination with a wide range fine step voltage 'tacts, said movable contacts of said coarse unit being connected to the tapped winding of said fine unit, an electrical control system for synchronizing said movable contacts comprising: a first current limiting means con- 7 nected to a power supply and responsive to bridging and inonbridging positions of said coarse movable contacts;

' land a second current limiting means connected between With the transfer switches now in their coarse said first current limiting means and each said motor ing with a-pluraliy of taps connected to circular arranged stationary contacts and a pair of movable contacts driven by a motor for successively engaging said stationary con-' 'tacts, said movable contacts of said coarse unit being While only oneemb'odiment of connected'to the tapped winding of said fine unit, an elecregulator having a'coanse step tap changing unit and a fine step tap changing unit, each said unit having a winding with a plunality'of taps connected to circular arranged stationary contacts: and a motor driven pair of movable contacts driven by a motor for successively engaging said stationary contacts, said movable contacts of said coarse unit being connected to the tapped winding of said fine unit, an electrical control system for-synchronizing said movable contacts comprising: a first set of conductors connected to a power supply with a portion thereof being conductive only in response to bridging positions of said coarse movable contacts, the remainder of said conductors beingconductive only in response to nonbridging positions of said coarse movable contacts; each said motor having a pairof windings with each winding connected to one each or said bridging and nonbridging 'responsive conductors by two of asecond set of conductors; said second set of conductors changing from conductive to nonconductive response to the position of said fine movable contacts relative to said fine stationary contacts whereby Load current in said regulator is maintained throughout cycling of said fine movable contacts by said fine unit motor. j

6. In combination with a wide range fine step voltage regulator having a coarse step tap changing unit and a fine step tap changing unit, each said unit having a winding with a plurality of taps connected to circular arranged stationary contacts and a pair of movable contacts driven by a motor for successively-engaging said stationary contacts, said movable contacts of said coanse unit being connected to the tapped winding of said fineunit, an electrioalcontnol system for synchronizing said movable con tacts comprising: a first set of switch carrying parallel connected conductors connected to -a power supply with a portion thereof {being conductive [only .in response tobridging positions of said coarse movable contacts, the

remainder of said conductors being conductive only in response tononbrid-ging positions of said coarse movable contacts; eachflsaid' motor having a pair of windings with eachwinding connected to one each of said bridging and nonbrid-ging responsive conductors by two (of a second set response to the position of said fine movable contacts relative to said finestationary contacts whereby uniform voltage steps and load current are maintained throughout successive cycling of said fine movable contacts by said fine unit motor.

7. In combination with tawide range" fine step voltage regulator having a coarse step-tap changing unit and a fine step tap changing unit, each said u'nithaving a winding with a pluna lity of taps connected to cincular arranged stationary contacts and a pair of movable contacts driven by a-motor for successively engaging said stationary contacts, said movable contacts of said coarse unit being connected to the tapped winding of said fine unit,an elec trical control system for synchronizing said movable con tacts comprising: :a first set of switch carrying parallel connected conductors connected to a power supply with a portion thereof being conductive only in response to v bridging positions of said coans-e movable contacts the remainder of said conductors being conductive only in response to nonbridging positions or said coarse movable contacts; each said motor having a pair of windings with each winding connected to one each of said bridging and nonbridging responsive conductors by two ot" a second set of switch carrying conductors in series with said first set of conductors; said second set of conductors changing from conductive to non-conductive in response to the position of said fine movable contacts relative to said fine stationary contacts whereby load current in said regulator is maintained throughout successive cycles [of said fine movable contacts by said fine unit motor.

8. In combination with a wide range fine step voltage regulator having a coarse step tap changing unitand (a fine step tap changing unit, each said unit having a winding with a plurality of taps connectedto circular larnanged stationary contacts and [a pair of movable contacts driven by a motor tor successively engaging said stationary contacts, said movable contactswoi said coarse unit being consaid fine stationary contacts whereby load currentin said regulator is maintained during driving of said movable contacts by said motors; a transfer mechanism having a motor for driving said bypass switches; and switching means connecting said transfer motor to said power supply at a predetermined position-of said fine movable contacts whereby load current is maintained throughout cyclingof said movable contacts and operation of said transfer mechanism.

Q References Cited in ,thefile of this patent UNITED'STATES PATENTS 2,480,589 McKenney Aug. 30, 1949' 2,933,671

Prescott et al Apr. 19, 1950 

1. A WIDE RANGE FINE STEP VOLTAGE REGULATOR COMPRISING A COARSE STEP TAP CHANGING UNIT AND A FINE STEP TAP CHANGING UNIT MECHANICALLY INDEPENDENT OF EACH OTHER, EACH SAID UNIT HAVING A WINDING WITH A PLURALITY OF TAPS WITH CIRCULAR ARRANGED STATIONARY CONTACTS CONNECTED THERETO AND A PAIR OF MOVABLE CONTACTS DRIVEN BY A MOTOR FOR SUCCESSIVELY ENGAGING SAID STATIONARY CONTACTS, SAID MOVABLE CONTACTS OF SAID COARSE UNIT BEING CONNECTED TO THE TAPPED WINDING OF SAID FINE UNIT, AND AN ELECTRICAL CONTROL SYSTEM FOR SYNCHRONIZING EACH SAID MOTOR AND SAID MOVABLE CONTACTS IN EACH SAID UNIT COMPRISING CURRENT LIMITING MEANS RESPONSIVE TO THE POSITIONS OF SAID MOVABLE CONTACTS RELATIVE TO THEIR RESPECTIVE STATIONARY CONTACTS WHEREBY LOAD CURRENT IN SAID REGULATOR IS MAINTAINED THROUGHOUT CYCLING OF SAID MOVABLE CONTACTS BY EACH SAID MOTOR. 